Constant pressure type contact spring



Dec. 14, 1965 w. c. FACKLER ETAL 3,223,793 CONSTANT PRESSURE TYPE CONTACT SPRING Filed March 25, 1964 INVENTORS Warren C. /er

Carl E. Michel 4 /%%l:

Afforn United States Patent Ofiice 3,223,793 Patented Dec. 14, 1965 3,223,793 CONSTANT PRESSURE TYPE CONTACT SPRING Warren C. Fackler and Carl E. Michel, Cedar Rapids, Iowa, assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Mar. 25, 1964, Ser. No. 354,666 6 Claims. (Cl. 200-11) This invention relates in general to electrical switch slide contacts and in particular, to a novel slide contact capable of maintaining uniform contact force.

In electrical circuitry slide contacts presented many problems. There is a tendency for contact to be intermittent between the stationary member and the slide contact due to build-up of dirt or other foreign substances. At other points too much pressure may exist between the slide contact or stationary member which causes excessive wear.

At times a stationary member may constitute a wire which varies in distance from the center axis of the slide contact resulting in non-uniform force between the slide contact and the stationary member.

It is an object of the present invention therefore, to provide a novel slide contact capable of exerting uniform force which does not vary if the fixed contact has a variable distance to the support axis of the slide contact.

Another object of the invention is to provide an improved slide contact which utilizes torsional and bending forces to obtain uniform contact force.

A feature of this invention is found in provision for a slide con-tact having a first portion attached to a rotating shaft and formed with a contact point which extends from a bend on a line parallel to a radius of the supporting shaft.

In this invention a slide contact capable of exerting uniform force on a stationary member which has a variable distance from the support axis has an extending portion of variable cross sectional area. A contact point is formed on a bent portion that is bent from the extending portion on a line parallel to the radius of the support ing shaft.

Further features, objects and advantages of the invention will become apparent from the following description and claims when read in view of the accompanying drawing, in which:

FIGURE 1 is a perspective view of a slide contact according to this invention,

FIGURE 2 is a plan view of the slide contact, and

FIGURE 3 is a side view of the invention.

FIGURE 1 illustrates an insulating plate which is formed with suitable mounting holes 11, 12 and 13 and which has attached to its surface a variable inductance fixed contact 14 which terminates at one end at contact post 16 and has a second end 17. A shaft 18 is rotatably supported by suitable bearing means 20 from the insulating plate 10 and carries a knob 19.

A collar 21 is attached to the shaft 18 and supports a pair of condenser plates 22 and 23 which in combination with a fixed plate 24 which is supported by contact post 16 form an air gap condenser.

The novel constant pressure slide contact of this invention is designated generally by numeral 26 and is attached to collar 21 at the semi-circular portion 37. The attachment can be made by solder or some other well-known means. A first extending portion 27 of contact 26 is tapered and is formed with a first ridge 28 along one edge and extends outwardly from the collar 21. The other edge of portion 27 is formed with a ridge 29 which terminates prior to the end of the slide contact. A portion 31 is bent 'backwardly along a line 32 and is formed with a dimpled contact portion 33. The

bend 32 lies on a line parallel to a radius of shaft 18. The dimpled contact portion 33 engages the fixed contact 14. The slide contact 26 in combination with the contact 14 form a variable inductor.

The condenser and variable inductance thus constructed form a tank circuit in which the capacitance and inductance may be varied by rotating the shaft 18 by knob 19. Since as clearly shown in FIGURE 2, the fixed contact 14 does not maintain a fixed distance from the shaft 18 a problem is presented in obtaining uniform contact pressure between the slide contact and the member 14 as the shaft 18 is rotated. The novel spring contact 26 of this invention solves this problem by using combined bending and torsional motion of the spring contact of this invention so that uniform spring contact force is obtained. The torsional force is created at the narrow point 34 of the contact 26 and a cut 36 is made into the material of the slide contact so as to reduce its cross sectional area at this point and allow torsional motion. This is facilitated by tapering the portion 27.

The bending force occurs between the line 32 and the dimpled contact portion 33.

Such a structure produces a constant spring force along any point of dimpled'surface 33 and the force does not vary with distance from the shaft 18. This means that as the fixed contact 14 varies in distance from the shaft 18 the contact pressure between the dimpled portion 33 and contact 14 will remain constant. The bending action is restricted mainly to surface 31 which lies between the bend 32 and the dimpled portion 33.

It is found that with this present invention the spring rate of the contact is low, thus decreasing sensitivity to axial displacement relative to the inductance wire 14. This results in better contact force, ease of assembly and eliminates low and excessive forces previously resulting from an attempt to obtain good contact under all conditions. By maintaining the contact force substantially constant mechanical failures have been substantially reduced. Under laboratory tests the present tuner satisfactorily operated more than three times as long as conventional slide contacts.

Although this invention has been described with respect to a particular embodiment, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

We claim:

1. A contact arrangement comprising a sliding contact and a fixed contact, said sliding contact being attached to a supporting shaft and having a tapered portion attached to the shaft and extending therefrom and becoming narrower with distance away from the shaft, a bent portion extending from the tapered portion and adapted to engage said fixed contact with constant pressure, a first ridge formed along a first edge of said tapered portion and a second ridge formed along a second edge of the tapered portion, engagement of said bent portion with said fixed contact resulting in bending and torsional forces in the slide contact as it varies longitudinally relative to the shaft.

2. In apparatus according to claim 1 wherein said second ridge is shorter than the first ridge and a notch is formed in the tapered portion adjacent the end of the second ridge away from the shaft to facilitate torsional bending in the slide contact.

3. In apparatus according to claim 2 wherein the end of the bent portion away from the bend is formed with a dimpled portion on a line substantially radial relative to the shaft.

4. In apparatus according to claim 3 wherein said slide contact and shaft are rotatably supported by a supporting means, a fixed electrical member attached to the supporting means and engaged by the dimpled portion of the slide contact, and said point of contact variable with rotation of said shaft.

5. In apparatus according to claim 4 wherein said fixed electrical contact on the support means has a variable distance from the center of the shaft.

6. A contact capable of exerting constant pressure comprising attaching means for attaching said contact to a shaft, a first tapered portion adjacent to said attaching means and becoming narrower as the distance increases away from said attaching means, bent portion attached to said tapered portion and bent from said tapered portion along a line substantially parallel to a radius of said attaching means, said tapered portion and said bent por- 4 e tion being substantially parallel, said bent portion formed with a contact area along its end away from the bend, and said tapered portion having a first ridge along one edge and a second ridge along another dge.

References Cited by the Examiner UNITED STATES PATENTS 1,140,434 5/1915 Andres 200-11 X 2,682,643 6/1954 Thias 200-11 X 2,816,182 12/1957 Weaver 200-11 3,030,460 4/1962 Huetten et al 200--11 KATHLEEN H. CLAFFY, Primary Examiner. JAMES R. SCOTT, Assistant Examiner. 

1. A CONTACT ARRANGEMENT COMPRISING A SLIDING CONTACT AND A FIXED CONTACT, SAID SLIDING CONTACT BEING ATTACHED TO A SUPPORTING SHAFT AND HAVING A TAPERED PORTION ATTACHED TO THE SHAFT AND EXTENDING THEREFROM AND BECOMING NARROWER WITH DISTANCE AWAY FRON THE SHAFT, A BENT PORTION EXTENDING FROM THE TAPERED PORTION AND ADAPTED TO ENGAGE SAID FIXED CONTACT WITH CONSTANT PRESSURE, A FIRST RIDGES FORMED ALONG A FIRST EDGE OF SAID TAPERED PORTION AND A SECOND RIDGE FORMED ALONG A SECOND EDGE OF THE TAPERED PORTION, ENGAGEMENT OF SAID BENT PORTION WITH SAID FIXED CONTACT RESULTING IN BENDING AND TORSIONAL FORCES IN THE SLIDE CONTACT AS IT VARIES LONGITUDINALLY RELATIVE TO THE SHAFT. 